The present invention concerns an apparatus for controlling the rotational speed of the spindles of a spinning preparatory machine equipped with spindles and with flyers operatively coordinated thereto, as a function of the increasing bobbin diameter. The control apparatus contains a variator for driving the spindles, and such variator can be infinitely varied by using a control shaft which is stepwise rotated.
In a spinning preparatory machine of this type, also called roving frame or fly frame, a fibre roving is produced and is wound in parallel windings onto the bobbin of each spinning position, using a flyer. As the fibre roving is to be draftable as input material to be fed to the next processing step, a very low twist is imparted to it, barely sufficient for tensionless transfer of the fibre roving to a drafting arrangement of the subsequent processing step, but resulting in an undesirable faulty draft in the roving under the smallest tensile stress.
With such spinning preparatory machines it is necessary to drive both the spindle, and the flyer, which distributes the fibre roving over the bobbin surface and which flyer rotates coaxially with the spindle, and furthermore to precisely adjust the mutual rotational speeds.
In this arrangement the flyer, as a rule, rotates at a constant rotational speed, while the rotational speed of the spindle is adapted according to the increasing bobbin diameter: the spindle, in this arrangement, performs the reciprocating spindle rail stroke between two reversal points moving with respect to space as a function of the bobbin diameter, this traversing stroke ensuring for both the winding of the fibre roving in parallel windings onto the bobbin surface and the conical built or formed shape of the bobbin extremities.
The present invention deals with the problem of adapting the rotational speed of the spindle to the increasing bobbin diameter, and there is not specifically involved the reduction of the spindle rail traverse stroke as a function of the bobbin diameter.
The increase of the bobbin diameter, however, decisively depends on the technological properties of the roving produced, such as e.g. fibre type and quality, count (or linear density), twist, volume, etc. Experience has shown, that e.g. the volume of a roving of this type, or its cross-section respectively, depends on the air or climatic conditions, i.e. it can vary over time, and that also such minute variations already constitute a disturbing factor in the winding process, which is to be corrected using suitable means.
In the state of the art, countless propositions for controlling the rotational speed of a spinning preparatory machine of this type are known, in which machine, for obtaining the precision control which is required, usually a coarse control device and a fine control device are applied working in combination. Using the coarse control device, the best known form of which and that which is most universally utilized is a double-cone belt drive arrangement, the rotational speed of the spindle is roughly adapted to the geometric dimensions of the bobbin and in particular to its diameter. Using the fine control device, which frequently is in the form of a multi-member compensating rail, the speed ratio of the cone belt drive is influenced and a fine correction of the roving tension at different diameters of the bobbin is effected.
A solution of this type is shown, e.g. in Swiss Pat. No. 569,806. As a correcting rail here a control surface is used, which over the whole zone of the belt shifting of the cone belt drive exerts a correcting influence thereon. In a solution of this type with a double cone belt drive arrangement, of course, also adaption of the average speed of the belt shifting movement to the roving volume is required, which as a rule is effected by insertion of a gear train with exchangeable gears. Typical for this solution is the application of an infinitely variable variator, which is adjusted by a control shaft, which is rotated stepwise. The disadvantages of this known solution reside in its poor operatability and in its complicated design. Setting the elements for the rough control (e.g. the change gear for shifting the double cone belt) as well as for the fine control is to be effected while the machine is at a standstill, as manipulations are performed at the gear train. The whole operation of adjusting the settings of the control elements, which is to be extended over several complete doff cycles, if the success of the adjustments effected is to be judged, is very time-consuming and complicated, and thus the spinning preparatory machine in many cases is not set optimally but to approximate accuracy only. The resulting faulty drafts in the roving and an increased number of roving breakages result in corresponding stoppages, causing downtime and deterioration in machine efficiency.
Also the adaption to the variable air conditions in the spinning room proves very problematic in view of the above mentioned operational disadvantages of the known devices.
A further disadvantage of the known device is seen in that it requires a great deal of maintenance, particularly cleaning and lubrication operations. Furthermore, in a device of such type the disadvantage is to be mentioned that the control elements are to be equipped with particular resetting elements, using e.g. the belt of the double cone belt drive which is to be brought back into its starting position after the belt has been released while the machine is at a standstill. For this purpose, e.g. a releasing device for the cones and a separate resetting motor, which are active merely during the very short time period of the resetting operation, are required, the device thus becoming still more complicated and expensive.
Solutions similar to the one described here are described e.g. in French Pat. No. 15 66 512 and in German Patent Application No. 12 91 664. For these the disadvantages cited in connection with the above mentioned state of the art also apply.
In other known devices for a spinning preparatory machine, control of the rotational speed of the spindle is effected in that the roving tension is maintained constant, which implies that the roving tension is measured.
This control technique, based only on the winding conditions at individual spinning positions, requires a relatively complex installation of measuring instruments, but does not ensure that the roving tension is correct at the other spinning positions. If, unfortunately, just the one spinning position at which the roving tension is measured, runs extremely tight or extremely slack, all other spinning positions which might run correctly are corrected correspondingly in such a manner that, at these spinning positions, the complexity of the arrangement notwithstanding, optimum spinning conditions are not obtained.